One type of earth boring bit, called “impregnated bit” is used for drilling relatively hard, abrasive, or hard and abrasive rock formations, such as sandstones. An impregnated bit has a crown or cutting face composed of diamond impregnated matrix. The matrix may comprise super abrasive cutting particles, such as natural or synthetic diamond grit, dispersed within a matrix of wear resistant material. The wear resistant matrix typically comprises a tungsten carbide powder infiltrated with a copper-based binder.
The crown is molded to define blades having a variety of shapes. Flow channels, also called “junk slots”, are located between the blades. Ports are located in some of the channels. Each port extends through the shell of the crown to an interior cavity for discharging drilling fluid pumped down the drill string.
The ports are fixed in diameter and they tend to wear or wash out during use. Using replaceable nozzles is known for some types of earth boring bits, particularly rolling cone bits. However, the widths of the flow channels are not sufficient for these types of nozzles.